The role of variation in cholesterol absorption on plasma lipids, cholesterol synthesis and, ultimately, the development of atherosclerosis is largely unstudied. The purpose of this study is to assess the effects of differing biliary bile acid composition, dietary fatty acid composition and differences in plasma cholesterol on cholesterol absorption, cholesterol fractional synthetic rate and LDL-receptor and HMG-CoA reductase mRNA in groups of healthy adults. This outpatient study involves CRC preparation of meals with close supervision of subject compliance, collection of duodenal drainage after a standardized meal stimulus, measurement of cholesterol absorption utilizing the dual isotope technique with measurement of isotope ratios in serum and the measurement of the fractional synthetic rate for cholesterol in red blood cells.